BY R. J. TILLYAHD. 3^3 



Spot where it is common, a careful search will reveal the 

 existence of a dimorph. As regards /. delicata, this insect differs 

 greatly both in size and colouration from the other two; however, 

 I was confident that a dimorphic form would be found to exist. 

 But, in spite of its abundance all over the Eastern States, a 

 careful search for many months failed to reveal the desired form. 

 It was only during my trip to Western Australia, in January 

 last, that I was successful in discovering the dimorphic female. 

 It is a distinctly rare form, and where it occurs, it numbers only 

 about 10% of the females taken; whereas in the case of hetero- 

 slicta the dimorph occurs in every locality and is nearly as 

 common as the ordinary form. 



As regards the genus Agriocneniis, on account of the rarity of 

 most of the species, my data are necessarily incomplete, but they 

 are suflficient to show the existence of a series of dimorphic 

 females of a different type from those of Ischnura. The dimorphs 

 of Ischnura in Australia are male-mimicking, but in other 

 countries, dimorphs of this genus liave been recorded, known as 

 " orange " forms from their prevailing colour. The dimorphs of 

 A gi^iocne mis ma.y -aI^o be classed as " orange " or "red " forms, 

 and are remarkable for showing not the slightest resemblance 

 either to the male or to the ordinary form of the female, so much 

 so that in some cases I have been for a long time deceived as to 

 the identity of the insect (see Agriocnemis pruinescens below). 

 The series is very incomplete in this genus, and in onl}' one 

 species have I found both forms of the female; but in the other 

 species, the one form of female that is so far known to occur is 

 sometimes an ordinary form and sometimes an "orange" or 

 " red " form. Hence I have arranged all the known females into 

 two groups, feeling certain that, as in the case of /. delicata, a 

 careful search for a second form of the female, where still 

 wanting, will be well rewarded. There is of course also the 

 possibility that amongst these extremely rare species of Agrioc- 

 nemis one of the two forms of female has already died out, thus 

 accelerating the final demise of the species. 



